1. Field of the Invention
The present invention relates to a radiating film or radiating sheet containing a polymer material, and more particularly to a radiating sheet for releasing heat efficiently by inserting to fill in a gap between a heat generating element of electric appliance such as power transistor, hi-density integrated circuit, plasma display panel (or PDP glass panel in some cases), and a heat sink such as an aluminum chassis (or aluminum panel in some cases). The invention also relates to a PDP panel formed by inserting a radiating sheet between a glass panel and an aluminum panel.
2. Description of the Related Art
Recently, as electronic appliances are enhanced in performance and reduced in size, the trend of higher density and higher function of semiconductors and other electronic components is progressing. As the electronic components are becoming higher in density and function, a larger amount of heat is generated from the electronic components themselves. If this heat is left over, the quality of the electronic components deteriorates, or the electronic components may be damaged, and therefore the device or mechanism for efficiently removing the heat generated by electronic components is indispensable. For example, if a heat generating element is a PDP glass panel, when the PDP panel is illuminated, heat is generated and uneven temperature occurs partly, which may lead to breakage of glass.
At the present time, as a method of removing heat generated from heat generating elements in an electronic appliance, it is known to insert a radiating material between a heat generating source (or heat generating element in some cases) of the electronic appliance and an aluminum radiating fin. The radiating material used herein includes silicone radiating grease, silicone radiating sheet, acrylic radiating pressure-sensitive adhesive sheet, urethane radiating pressure-sensitive adhesive sheet, and others. These radiating materials are prepared by blending flexible polymer materials and fillers of high heat conductivity. Such radiating materials are known to have also a shock absorbing effect besides the heat releasing effect.
In the radiating material using such conventional silicone radiating grease or silicone radiating sheet, the heat releasing performance is excellent because it can be filled with a large amount of radiating filler large in heat conductivity, but there is no function as pressure-sensitive adhesive, and it must be fixed between the aluminum chassis and heat generating source by screwing or other means, and in the manufacturing process of electronic appliances, it was hard to fix if desired to fix the silicone radiating sheet to heat generating source of the CPU and the like or aluminum chassis and the like.
On the other hand, the acrylic radiating pressure-sensitive sheet and urethane radiating pressure-sensitive adhesive sheet are excellent in fixing performance as compared with the silicone radiating grease or silicone radiating sheet, but the heat conductivity is extremely low as compared with that of silicone radiating material, and heat could not be transmitted sufficiently to the aluminum chassis.
Or, for fixing the PDP glass panel and aluminum heat sink, a double-sided acrylic adhesive tape may be adhered to the end portions and a silicone radiating sheet may be used in the center, but in this case the adhering effect and radiating effect were low.
In the light of the problems of such radiating sheets, it was also proposed to use a radiating sheet having a performance of pressure-sensitive adhesive, capable of being fixed between the heat generating source and heat sink such as aluminum chassis, and also excellent in radiating performance. In this sheet, a pressure-sensitive adhesive layer was adhered to the surface of the silicone radiating sheet or part of the surface, and acrylic adhesive or urethane adhesive was mostly used in the pressure-sensitive adhesive layer.
However, in the case of a radiating sheet for a PDP, for example, the radiating sheet is inserted between the PDP glass panel and aluminum chassis, but the aluminum chassis used herein is not a mere flat plate, but is a structure having an irregular shape for mounting IC parts, or having holes and the like for passing wires, and is formed by die casting or pressing of aluminum plate.
Since the aluminum is distorted in this forming process, if the radiating sheet is compressed and fitted tightly between the aluminum chassis and PDP glass panel, in the conventional radiating material, an air layer is formed between the PDP panel glass and radiating sheet, or between the aluminum chassis and the radiating sheet, and a partial temperature unevenness occurs in the PDP glass panel, and the glass maybe broken. Such uneven distribution of heat is a major cause of breakage of PDP glass.
This problem is not limited to the heat generating element of the PDP glass panel, but it also causes to lower the contact rate with the radiating sheet, heat generating element and heat sink.
Accordingly, there has been a keen desire for a radiating sheet which contacts tightly with a heat generating element such as the PDP glass panel and the heat sink such as aluminum chassis, and is uniform in heat distribution and is excellent in heat transfer to the heat sink of aluminum or the like.
The invention is achieved in the background described above, and it is hence an object of the invention to provide a radiating sheet capable of preventing defective contact due to poor precision of aluminum panel, and releasing heat efficiently and uniformly from the heat generating element such as the PDP glass panel. It is another object to present a radiating sheet contacting tightly with a heat generating element and a glass panel. It is a further object of the invention to present a PDP panel formed by inserting such radiating sheet between a glass panel and an aluminum panel.
The invention relates to a radiating sheet for contacting tightly with a heat generating element such as a PDP glass panel and a heat sink such as aluminum chassis, and distributing the heat uniformly, and the object of the invention is achieved by a radiating sheet characterized by forming a spongiform radiating element by impregnating any one of radiating materials selected from the group consisting of a radiating gel and a radiating grease, in a radiating base material having continuous foams.
Preferably, the radiating base material may be a urethane foamed material, or the radiating gel may be composed of a silicone gel and a filler. The radiating grease may be a silicone radiating grease.
In another aspect, a spongiform radiating element/radiating material layer may be formed by coating whole or part of a surface of a spongiform radiating element with a silicone radiating sheet, or a spongiform radiating element/aluminum foil layer may be formed by adhering an aluminum foil layer to a spongiform radiating element.
Preferably, an acrylic pressure-sensitive adhesive may be applied to the surface of thus obtained radiating sheet of a spongiform radiating element, or layered radiating sheet forming a spongiform radiating element/radiating material layer or a spongiform radiating element/aluminum foil layer.
Preferably, a cut may be formed in the surface of the spongiform radiating sheet, layered radiating sheet, or radiating sheet on which an acrylic pressure-sensitive adhesive is applied.
By forming such radiating sheet between a glass panel and an aluminum panel, the PDP panel as the object of the invention is obtained (in the invention, the PDP panel refers to one having a radiating sheet inserted between a PDP glass panel and a heat sink such as aluminum panel).